During routine maintenance on various structures such as bridges or buildings, the previous paint coatings are abrasively removed to Provide a secure surface for the new primer and topcoat systems. Typically, abrasive blasting is used once the existing paint coating on a structure has deteriorated beyond repair. In abrasive blasting, a stream of high pressure air is used to carry the abrasive particles to the structure surface at a high speed. The impact of the abrasive with the surface chips off the old paint coatings and cleans the steel surface providing an excellent base for applying the new coating. The spent abrasive particles combined with the paint chips fall to the ground where it traditionally was raked up and either disposed of at the job site or dumped in sanitary landfills.
Recently, a crisis has emerged in the field of abrasive blasting as State and Federal environmental regulators have identified the blasting residue as a potentially hazardous waste due to the lead-based paint used to paint various structures in past years. Estimates vary, but typically 50-75of all residues from tank and structural steel blasting fail the EP (extraction procedure) Leach test used by the U.S. EPA (United States Environmental Protection Agency) as one of the methods to characterize potentially hazardous waste material. Although lead is the most common toxic metal identified in abrasive blasting residues, they may also contain elevated amounts of chromium, arsenic, mercury, and other hazardous materials, possibly in concentrations sufficient to result in an unsatisfactory determination in the EP Leach test.
Two types of problems are associated with the abrasive blasting of paint from structures. First, the spent abrasive particles and the removed paint must be contained during blasting and second, the blasting residue must be disposed of properly. The problem of containment can be achieved by various engineering controls presently available. The present invention helps in accomplishing the problem of disposal.
Currently, hazardous waste disposal is very expensive. Moreover, new regulations are expected which will increase the cost of hazardous waste disposal and encourage efforts to reduce the volume of hazardous waste by treating it prior to disposal to remove as much nonhazardous waste as possible. The reduction in the amount of hazardous waste becomes a paramount consideration as available capacity in approved hazardous waste landfills is rapidly depleted.
Moreover, even when the residue from blasting does not contain hazardous material, it is often desirable to reuse or recycle the paint chips and the abrasive particles for economic savings. However, the recycled abrasive particles lose their effectiveness as the paint content increases. There are various devices that reprocess abrasive residues, generally using a mechanical sizing process. See the article entitled "Current Blasting Technologies", by John Lunardini, at pp. 93-108 of the Lead Paint Removal Proceedings of the SSPC Symposium, Vol. SSPC 88-01 (1988) published by the Steel Structures Painting Council. A significant improvement over these devices would be obtained if the paint particles could be separated from the abrasive media. However, the variable nature of the residue materials from different sites which result from differing paint compositions, rust and iron contamination, as well as the varying blasting abrasives used, complicates the physical separation of the abrasive particles from the paint residue and prevents the separation from being economically and feasibly achieved.
It would be technically desirable, as well as economically and environmentally prudent, to have an efficient method of separating the hazardous paint component from the recyclable, reusable, or otherwise safely disposable blasting abrasive media.